The current invention relates to a method and apparatus for defibrillating cellulose fibres. The defibrillation is achieved through single and multiple passes of a raw or pre-processed cellulose fibre slurry, with a preferred solid material consistency range of 35% to 55%, through twin-screw fibre processing machines. During this processing operation, fibre slurries are optionally further enhanced with additional fibre and mineral additives to optimise performance of the material for specific end purposes.
The hyper defibrillated fibre slurry produced is defined as one reaching a Schopper-Riegler (SR) level of between 67° SR and 88° SR and/or producing a pressed, dried board with a density of preferably at least 850 kg/m3. Compared to traditional defibrillating methods, like single disc, multi-disc or conical refiners, advantages of the invention are significant energy and time savings, higher comparable output, and a very wide dry fibre consistency range of between 10% and 80%.
As used in this application, the term ‘consistency’ is a paper making term and refers to the amount of dry fibre in water suspension expressed as a percentage.
The current invention relates to a new method for the treatment of compositions comprising cellulose fibres into compositions comprising cellulose microfibers. The composition comprising cellulose microfibers obtained by the method according to the invention can now suitably and economically be used in producing, for example, 3-dimensional objects, wall and floor boards, wall and floor tiles and which have a high density of at least 850 kg/m3, with a preferred minimum of 1200 kg/m3.
Processes for opening, beating or defibrillating pulp to obtain fibrillation, increased surface area, increased accessibility and fine particle size have long been known. Ball mills are used for preparing cellulose of several tens of microns in dimension. Studies have indicated that such ball milling breaks the chemical bonds of the cellulose during the dividing process.
It is also known to grind cellulose in water under pressure to produce a micro-cellulose with a particle size of less than one micron. In the case of cellulose derivatives, cold milling of the derivatives in liquid nitrogen is also disclosed in the prior art. Sonic pulverization with a ball mill is also a known method of producing cellulose in extremely fine particle size.
Finely divided celluloses are also produced in the traditional processes used in manufacturing mechanical pulps, fibreboard and paper pulp. Normally, however, these traditional processes involve the use of additional chemical treatment to cellulose pulps, such as for example, acid hydrolysis, which chemically alter or degrade the prepared cellulose pulps.
In the paper industry, it is known that paper strengths are directly related to the amount of beating or refining which the fibres receive prior to formation. However, beating and refining as practiced in the paper industry are relatively inefficient processes and large amounts of energy are expended to gain relatively minor amounts of fibre opening and fibrillation.
GB2066145 describes a process for preparing micro-fibrillated cellulose, comprising passing a liquid suspension of fibrous cellulose through an orifice in which the suspension is subjected to a pressure drop of at least 3000 psi and a high velocity shearing, followed by a high velocity decelerating impact and repeating the passage of said suspension through the orifice until the cellulose becomes a substantially stable suspension. The process converts the cellulose into micro-fibrillated cellulose without substantial chemical change. A particularly suitable device for carrying out the process is a high pressure homogenizer. The liquid suspension comprising fibrous cellulose preferably contains no more than 10% by weight of cellulose.
EP0402866 describes micro-fibrillated material comprising fibres having a variety of thicknesses, having a Schopper-Riegler of 40° SR or greater, having a T valve of 15 or greater when the fibres are formed in a filter sheet. The materials are obtained using a high-pressure homogenizer. For example, it is described that using refined linter (Vackai HVE) as a raw material, a 2% suspension of cellulose in water is obtained by pre-treatment so that it can pass through the nozzle of the apparatus. The suspension is charged into a high-pressure homogenizer (Gaulin 15M-8TA) at ordinary temperature, and treated at a pressure of 500 kg/cm2 G for four times. The result and suspension of micro-fibrous material is diluted to a concentration of 0.2%.
U.S. Pat. No. 6,379,594 describes a process for producing a work piece, comprising providing raw cellulose-containing and fibrous material; adding water to the raw material; finely chopping the raw material in a machine by continuously grinding the raw material with a total energy expenditure of at least 0.5 kWh/kg, based on dry weight of the raw material, into a microfiber pulp having an increased internal fibre surface and an increased degree of interlinking; forming the microfiber pulp to provide a shaped body; and drying the body by removing water therefrom to harden and form a work piece, without admixture of bonding agents to the microfiber pulp and without use of external pressure. In this way, a moldable microfiber pulp with very diverse fibre lengths and fibril sizes develops, which pulp has the characteristic of hardening to form a subsequently deformable fibre material with high density (up to a specific gravity of 1.5) and strength without the admixture of adhesives or chemical additives and without the use of pressure, through drying and the associated shrinkage. The examples disclose that the cellulose-containing materials used in the method are taken up in watery solutions with a dry substance between 5 and 8% by weight.
However, the above processes have only a limited application as the material obtained has the disadvantage of requiring too high an energy input to be economically feasible (see the Examples) for use of such materials in forming, for example, 3-dimensional objects, wall and floor boards, wall and floor tiles, and, in general, for larger surfaces.
The difference between pulping and defibrillation should also be appreciated. In pulping, lignin is removed from ligno-cellulosic materials to render the fibres suitable for paper and board making. In defibrillation the purpose is to raise a nap of individual fibrils making up the outer surface or wall of the fibre whilst, at the same time, attempting to maintain both the condition of the interior of the fibre and the fibre length.
It is therefore an object of the current invention to provide a more economically and environmentally friendly method and apparatus for providing compositions comprising cellulose microfibers, for example, comparable to those described in U.S. Pat. No. 6,379,594.
It has been found by the current inventors that the above mentioned problems(s) are solved by the method, compositions, apparatus and use according to the current invention.